一般都卜勒技術只能提供軸向的血流速度，而橫向流速可用都卜勒頻寬法來估計。傳統的都卜勒頻寬法估計方式須同時應用到都卜勒偏移頻率和最大都卜勒頻率，然而都卜勒偏移頻率容易受到樣本區域內流動變異的影響，而降低估測橫向流速的正確性。其中，導致正確性下降的兩個主要原因，一是樣本區域位置偏移，另一個是樣本區域長度改變，本論文利用模擬和實驗的方式來觀察其變化。結果顯示，位置偏移會造成都卜勒偏移頻率有低估的情形，最大都卜勒頻率則保持不變，最後導致都卜勒頻寬會有超估情形產生。與位置偏移所受到的影響相比，樣本區域長度變化對橫向流速的估測影響較小。本論文提出差值最大都卜勒頻率法來解決位置偏移時所造成的誤差情形。此法是利用兩個不同聲束寬度的超音波聲束觀察血液的流動，用相對應的差值最大都卜勒頻率來估測橫向血流的速度。本論文的結果證明利用差值最大都卜勒頻率法時，即使樣本區域位置偏移，橫向流速的估測依然能保持其正確性與穩定性。

Conventional Doppler technique can only provide the axial velocity of blood flow. One Approach of transverse flow estimation is using Doppler Bandwidth. Traditional Doppler Bandwidth estimation must use Doppler shift frequency and maximum Doppler frequency. However Doppler shift frequency is affected easily by flow variation within the sample volume. It made accuracy of Doppler-bandwidth-based transverse flow estimation to decrease. Two factors that may lead to the Doppler spectral change were considered in this study. One is the position offset of the sample volume and the other is the length of the sample volume. Experimental and simulate data were collected. Results indicate that the position offset may result in severe underestimation of Doppler shift frequency, and Maximum Doppler frequency is almost constant. Consequently, Doppler bandwidth is overestimated when it is determined by the difference between Doppler shift frequency and maximum Doppler frequency. Compared to the position offset, influence of the length of sample volume on the Doppler bandwidth is minor. To overcome this problem, a novel method which is based on the differential maximum Doppler frequency is proposed. Specifically, two beams with different beam widths are simultaneously generated to observe the blood flow and the difference between the corresponding maximum Doppler frequencies is used to estimate the transverse velocity. It is demonstrated that the accuracy and stability of transverse estimation are significantly improved by the proposed method even when the position offset is present.

[1] Flemming Forsberg, PhD, ”Ultrasound imaging of angiogenesis,” Bioengineering Conference, 2002. Proceedings of the IEEE 28th Annual Northeast, 20-21 April 2002 Page(s): 291 – 292.
[2] 原者：Vincent P. Coletta 編譯：李端真、周嘉宜、李景明、邱久逵、何武信、林建德、倪紹仲和姬梁文, “物理(下),” 高立圖書有限公司
[3] 編：日本超音波醫學會, 譯：李嘉明、李玉華, “新超音波醫學-醫用超音波的基礎,” 合記圖書出版社.
[4] Sheikh Kaisar Alam and Kevin J. Parker, “The Butterfly Search Technique For Estimation of Blood Velocity,” Ultrasound in Med. & Biol., Vol. 21, No. 5 , pp. 657-670, 1995.
[5] Pai-Chi Li, Member, IEEE, Chong-Jing Cheng, and Che-Chou Shen, ”Doppler Angle Estimation Using Correlation” IEEE Transactions On Ultrasonics,“ IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol 47, No. 1, Jan. 2000.
[6] Gabriele Guidi, Vernon L. Newhouse, Life Fellow, IEEE, and Piero Tortoli, “Doppler Spectrum Shape Analysis Based on the Summation of Flow-Line Spectra,” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol. 42. No. 5, September 1995.
[7] http://www.acuson.com.
[8] 李維寧, “高效能斑點追蹤技術及其在乳房超音波影像之應用,” 國立台灣大學電機工程學研究所碩士論文

[9] Ilmar A. Hein, “3-D flow velocity vector estimation with a triple-beam lens transducer-experimental results,” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol. 44, No. 1, January 1997.
[10] David Vilkomerson, David Lyons, and Thomas Chilipka, “Diffractive Transducers for Angle-Independent Velocity Measurements,” EchoCath, Inc., Princeton, NJ, USA
[11] Piero Tortoli, Gabriele Guidi and Vernon L. Newhouse “Improved blood velocity estimation using the maximum Doppler frequency,” Ultrasound in Med. & Biol., Vol. 21, No.4 , pp. 527-532, 1995.
[12] Bor-Ray Lee, Huihua Kenny Chiang, Cheng-Deng Kuo, Win-Li Lin, and San-Kan Lee, “Doppler angle and flow velocity estimations using the classic and transverse Doppler effects,” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol. 46. No. 1, Jan. 1999.
[13] Jørgen Arendt Jensen, “Ultrasound imaging and its modeling,” Chapter in. Fink et al. (Eds.): ”Imaging of Complex Media withAcoustic and Seismic Waves,” Topics in Applied Physics, Vol. 84, pp. 135-165, Springer Verlag, 2002.
[14] Bor-Ray Lee, Huihua Kenny Chiang, Yi-Hong Chou, Cheng-Deng Kuo, Jia-Horng Wang and San-Kan Lee, “Implementation of spectral width Doppler in pulsatile flow measurements,” Ultrasound in Med. & Biol., Vol. 25, No. 8, pp. 1221–1227, 1999.